Methods and systems for photocuring liquid with reduced heat generation using a digital light processing (DLP) light source

ABSTRACT

In vat polymerization printer, light is projected from a digital light processing (DLP) light source towards an opening in a tank containing photo-curable liquid resin. A mask is used to filter the light from the DLP light source, the mask having pixels configurable to be individually transparent or opaque to portions of the light from the DLP light source. In a build area of the tank, the filtered light is used to cure the photo-curable liquid resin so as to form a layer of a partially formed object. The operation of the DLP light source is synchronized with the operation of the mask, such that light from the DLP light source with high intensity is transmitted through the transparent pixels of mask and light from DLP light source with low intensity is blocked by the opaque pixels of mask. The mask may enhance the resolution of DLP light source.

RELATED APPLICATIONS

This application is a non-provisional patent application of and claimspriority to U.S. Provisional Application No. 63/262,674, filed 18 Oct.2021, which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to the printing of three-dimensionalobjects, and more particularly relates to reducing the heat impartedinto the liquid resin by the light source.

BACKGROUND

One obstacle encountered in the three-dimensional printing of objectsthat involves the curing of photo-curable liquid resin is the heating ofthe liquid resin. Not only is the curing of the liquid resin anexothermic reaction (which locally heats regions of the liquid resinwhere the curing takes place), but the irradiation of the mask by alight source, typically an ultra-violet (UV) light source, also causesheating of the mask. As the mask is located in close proximity to theliquid resin, any heating of the mask also leads to the further heatingof the liquid resin.

If the liquid resin temperature exceeds a critical temperature, portionsof the resin may start to cure even in the absence of UV light, leadingto defects in the printed objects. In prior approaches, to prevent theliquid resin temperature from exceeding this critical temperature, theprinting process may be periodically halted to allow the liquid resin tocool, with the consequence of reducing the throughput of the printingprocess. Also in prior approaches, a resin circulatory system may beemployed to cool the heated resin. While heat removal via a resincirculatory system may effectively achieve the desired effect ofcontrolling the liquid resin temperature, approaches described hereincontrol the temperature of the liquid resin through other or additionalmeans.

SUMMARY OF THE INVENTION

In one embodiment of the invention, the need to cool the liquid resin isreduced by reducing the degree to which the liquid resin is heated.While the heating of the liquid resin due to the exothermic reactionthat takes place during the curing of resin cannot be avoided, theheating of the mask can be reduced by selectively illuminating onlyregions of the mask with transparent pixels and/or minimizing theillumination of the regions of the mask with opaque pixels.

In one embodiment of the invention, light may be projected from adigital light processing (DLP) light source towards an opening in a tankcontaining photo-curable liquid resin. A mask may be used to filter thelight from the DLP light source, the mask having pixels configurable tobe individually transparent or opaque to portions of the light from theDLP light source. In a build area of the tank, the filtered light may beused to cure the photo-curable liquid resin so as to form a layer of apartially formed object. The operation of the DLP light source may besynchronized with the operation of the mask, such that light from theDLP light source with high intensity is transmitted through thetransparent pixels of mask and light from DLP light source with lowintensity is blocked by the opaque pixels of mask, minimizing theheating of the mask. Since the resolution of a DLP light source istypically lower than the resolution of the mask, the mask may also beused to enhance the resolution of DLP light source.

These and other embodiments of the invention are more fully described inassociation with the drawings below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example and without limitingthe scope of the invention, with reference to the accompanying drawingswhich illustrate embodiments of it, in which:

FIG. 1 depicts a schematic cross-section of a 3D printing system inwhich an object undergoes fabrication in a tank containing aphoto-curable liquid resin, in accordance with one embodiment of theinvention.

FIG. 2 depicts a schematic to visually represent the light from adigital light processing (DLP) light source (e.g., with varyingintensity in the spatial dimension) being filtered by a mask, before thelight reaches the build area of the tank of a 3D printing system, inaccordance with one embodiment of the invention.

FIG. 3 depicts a schematic to visually explain the synchronized controlof the DLP light source and the mask, in accordance with one embodimentof the invention.

FIG. 4 depicts a flow diagram of a process for printing a layer of apartially formed object using a 3D printing system in which light from aDLP light source is filtered by a mask before curing resin at a buildarea of a tank of a 3D printing system, in accordance with oneembodiment of the invention.

FIG. 5 depicts components of a computer system in which computerreadable instructions instantiating the methods of the present inventionmay be stored and executed.

DETAILED DESCRIPTION

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings that form a part hereof,and in which are shown by way of illustration specific embodiments inwhich the invention may be practiced. It is understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention. Descriptionsassociated with any one of the figures may be applied to differentfigures containing like or similar components/steps. While the sequencediagrams each present a series of steps in a certain order, the order ofsome of the steps may be changed.

FIG. 1 depicts a cross-section of three-dimensional (3D) printing system100 (also called a vat polymerization printer), in which electromagneticradiation (e.g., ultra-violet light) is used to cure photo-curableliquid resin 18 in order to fabricate object 22 (e.g., a 3D object).Object 22 may be fabricated layer by layer; that is, a new layer ofobject 22 may be formed by photo-curing a layer 31 of liquid resin 18adjacent to the bottom surface of object 22 (also called the buildarea), the object may be raised by extractor plate 20, allowing a newlayer of liquid resin 18 to be drawn under the newly formed layer; andthe process repeated to form additional layers.

The 3D printing system 100 includes tank 10 for containing the liquidresin 18. The bottom of tank 10 includes bottom opening 12 to allowelectromagnetic radiation 28 from digital light processing (DLP) lightsource 26 to enter into tank 10. DLP light source 26 may comprise a DLPlight projector, or a digital micromirror device (DMD) that isirradiated by a light source. While one DLP light source is depicted inFIG. 1 , it is possible that in other embodiments (not depicted),multiple DLP light sources may be employed to project electromagneticradiation into tank 10 at the same time, allowing a higher intensity ofelectromagnetic radiation to be achieved.

An optional radiation-transparent backing member 16 (e.g., borosilicateglass or a toughened glass such as an alkali-aluminosilicate glass ofapproximately 100 μm thickness) may be used to seal the tank opening 12(i.e., to prevent the photo-curing liquid polymer 18 from leaking out oftank 10), while at the same time, allowing electromagnetic radiation toenter into tank 10 in order to cure the liquid resin 18.

One challenge faced by 3D printing systems of the present kind is thatin addition to adhering to the object 22, newly formed layers tend toadhere to the bottom of tank 10. Consequently, when the extraction plate20 to which the object is attached is raised by height adjustor 30, thenewly formed layer could tear and/or become dissociated from the object22. To address this issue, a flexible membrane 14 may be disposedadjacent to backing member 16 (if present) or may form the bottom of thetank 10 (if no backing member is used). Flexible membrane 14 may beformed of silicone or another material, and optionally, coated with anon-stick material such as polytetrafluoroethylene (PTFE) to reduce thelikelihood for the newly formed layer to adhere to the bottom of tank10. The flexible membrane 14 is transparent (or nearly so) to thewavelength of radiation emitted by the DLP light source 26 so as toallow that radiation to enter into tank 10 in order to cure the liquidresin 18.

A mask 25 may be disposed adjacent to tank opening 12 to spatiallyfilter the radiation that is incident on layer 31, so that specificregions of the liquid resin 18, that correspond to the cross section ofthe object 22 being printed, are cured. Mask 25 may be a transmissivespatial light modulator, such as a liquid crystal display (LCD) with atwo-dimensional array of addressable pixels. As will be more clearlydescribed in the figures below, certain ones of the pixels may becontrolled to be transparent, while others may be controlled to beopaque. Transparent pixels allow radiation to pass through the mask 25at certain spatial locations of mask 25 and into tank 10, consequentlycuring portions of the liquid resin 18, while opaque pixels preventradiation from passing through certain spatial locations of mask 25.

Advantageously, DLP light source 26 may be configured to impartradiation with low intensity (e.g., less than 25% of the peak radiation,less than 10% of the peak radiation, less than 1% of the peak radiation,etc.) on opaque pixels so as to minimize the heating of mask 25 and inturn minimize the heating of resin 18. The radiation on transparentpixels is maintained with a high intensity (e.g., greater than 75% ofthe peak radiation, greater than 90% of the peak radiation, etc.) assuch radiation is needed to cure the resin 18 in build area 31. However,since the resolution of a DLP light source 26 typically is lower thanthe resolution of mask 25 (e.g., an LCD mask), the above relationship oflight intensity to opaque or transparent pixels may not hold for theopaque pixels at the perimeter of transparent pixel regions. For theopaque pixels at the perimeter of transparent pixel regions, theradiation from the DLP light source 26 may still be high and thus thefunction of those opaque pixels to block light is still carried out.Conceptually, the mask 25 enhances the resolution of DLP light source26, as described in more detail below in FIG. 2 . If not alreadyapparent, such selective radiation of mask 25 (and hence the minimizingof the heating of resin 18) is not possible with conventional lightsources that emit a uniform collimated beam of light which radiates allpixels of mask 25 with the same intensity of radiation irrespective ofwhether the respective pixels are transparent or opaque.

Controller 50 may be communicatively coupled to DLP light source 26,mask 25, and height adjustor 30 via control signal paths 38 a, 38 b and38 c, respectively (e.g., electrical signal paths). Controller 50 maycontrol the addressable pixels of mask 25 such that the transparentpixels of mask 25 correspond to a cross section of an object to beprinted. Similarly, controller 50 may control DLP light source 26 suchthat portions of the light from DLP light source 26 with high intensitycorrespond to a cross section of an object to be printed. Importantly,the operation of DLP light source 26 may be synchronized with theoperation of mask 25, such that light from DLP light source 26 with highintensity is transmitted through the transparent pixels of mask 25 andlight from DLP light source 26 with low intensity is blocked by theopaque pixels of mask 25. Such synchronized control by controller 50 isdescribed in more detail below in FIG. 4 .

Controller 50 may also control height adjustor 30 to control thevertical position of height extractor 20, and consequently of object (orpartially formed object) 22 that is affixed to height extractor 20.Using height extractor 20, the position of object 22 may be translatedin a direction perpendicular to an extent of the flexible membrane 14.

FIG. 2 depicts a schematic to visually represent light 28 from DLP lightsource 26 (e.g., with varying intensity in the spatial dimension) beingfiltered by mask 25 (more specifically, a column or row of pixels 25′from mask 25), before the filtered light 28′ reaches build area 31 (morespecifically, strip 31′ from build area 31) of tank 10 of the 3Dprinting system 100. For simplicity of illustration, a two-dimensionalslice through the 3D printing system 100 is being illustrated in FIG. 3, as shown by the inset which provides some context to the orientationof the two-dimensional slice. As shown in FIG. 3 , light 28 istransmitted from DLP light source 26, the light 28 having varyingintensity in the spatial dimension. Light 28 is filtered by mask 25,producing filtered light 28′. Light with high intensity (for the mostpart) passes through the transparent pixels of mask 25, whereas lightwith low intensity (for the most part) is blocked by the opaque pixelsof mask 25. Notice how the transitions of the light intensity aresharper in filtered light 28′, as compared to light 28, illustrating theincreased resolution provided by mask 25. The filtered light 28′ thencures resin 18 at the build area 31.

FIG. 3 depicts a schematic to visually explain the synchronized controlof DLP light source 26 and mask 25. At time instance t₁, light pattern302 a (with a high intensity portion 302 b and a low intensity portion302 c) is transmitted to DLP light source 26, and mask pattern 304 a(with transparent portion 304 b and opaque portion 304 c) is transmittedto mask 25. The shape of high intensity portion 302 b substantiallyresembles the shape of transparent portion 304 b at time instance t₁,demonstrating the synchronized control of DLP light source 26 and mask25 by controller 50. At time instance t₂, light pattern 306 a (with ahigh intensity portion 306 b and a low intensity portion 306 c) istransmitted to DLP light source 26, and mask pattern 308 a (withtransparent portion 308 b and opaque portion 308 c) is transmitted tomask 25. The shape of high intensity portion 306 b substantiallyresembles the shape of transparent portion 308 b at time instance t₂,further demonstrating the synchronized control of DLP light source 26and mask 25 by controller 50. At time instance t₃, light pattern 310 a(with a high intensity portion 310 b and a low intensity portion 310 c)is transmitted to DLP light source 26, and mask pattern 312 a (withtransparent portion 312 b and opaque portion 312 c) is transmitted tomask 25. The shape of high intensity portion 310 b substantiallyresembles the shape of transparent portion 312 b at time instance t₃,further demonstrating the synchronized control of DLP light source 26and mask 25 by controller 50. For simplicity of illustration, only onehigh intensity portion was depicted and only one transparent portion wasdepicted, but it is understood that in practice, one or more highintensity portions and one or more transparent portions may be present.

FIG. 4 depicts flow diagram 400 of a process for printing a layer of apartially formed object 22 using 3D printing system 100 in which lightfrom DLP light source 26 is filtered by mask 25 before curing resin 18at build area 31 of the tank 10. At step 402, light 28 from DLP lightsource 26 may be projected toward bottom opening 12 of tank 10containing liquid resin 18. At step 404, mask 25 may be used to filterlight 28 from DLP light source 26. As described above, in most instanceslight with high intensity from DLP light source 26 may be transmittedthrough the transparent pixels of mask 25, and light with low intensityfrom DLP light source 26 may be blocked by the opaque pixels of mask 25.However, at the “boundary regions” (i.e., the opaque pixels surroundingregions with transparent pixels), light with high intensity from the DLPlight source 26 may also be blocked by the opaque pixels of mask 25,thereby enhancing the resolution of DLP light source 26. At step 406,liquid resin 18 in build area 31 of the tank 10 may be cured by thefiltered light 28′ from the DLP light source 26 so as to form a layer ofa partially formed object 22.

As is apparent from the foregoing discussion, aspects of the presentinvention involve the use of various computer systems and computerreadable storage media having computer-readable instructions storedthereon. FIG. 5 provides an example of system 500 that may berepresentative of any of the computing systems (e.g., controller 50)discussed herein. Note, not all of the various computer systems have allof the features of system 500. For example, certain ones of the computersystems discussed above may not include a display inasmuch as thedisplay function may be provided by a client computer communicativelycoupled to the computer system or a display function may be unnecessary.Such details are not critical to the present invention.

System 500 includes a bus 502 or other communication mechanism forcommunicating information, and a processor 504 coupled with the bus 502for processing information. Computer system 500 also includes a mainmemory 506, such as a random access memory (RAM) or other dynamicstorage device, coupled to the bus 502 for storing information andinstructions to be executed by processor 504. Main memory 506 also maybe used for storing temporary variables or other intermediateinformation during execution of instructions to be executed by processor504. Computer system 500 further includes a read only memory (ROM) 508or other static storage device coupled to the bus 502 for storing staticinformation and instructions for the processor 504. A storage device510, for example a hard disk, flash memory-based storage medium, orother storage medium from which processor 504 can read, is provided andcoupled to the bus 502 for storing information and instructions (e.g.,operating systems, applications programs and the like).

Computer system 500 may be coupled via the bus 502 to a display 512,such as a flat panel display, for displaying information to a computeruser. An input device 514, such as a keyboard including alphanumeric andother keys, may be coupled to the bus 502 for communicating informationand command selections to the processor 504. Another type of user inputdevice is cursor control device 516, such as a mouse, a trackpad, orsimilar input device for communicating direction information and commandselections to processor 504 and for controlling cursor movement on thedisplay 512. Other user interface devices, such as microphones,speakers, etc. are not shown in detail but may be involved with thereceipt of user input and/or presentation of output.

The processes referred to herein may be implemented by processor 504executing appropriate sequences of computer-readable instructionscontained in main memory 506. Such instructions may be read into mainmemory 506 from another computer-readable medium, such as storage device510, and execution of the sequences of instructions contained in themain memory 506 causes the processor 504 to perform the associatedactions. In alternative embodiments, hard-wired circuitry orfirmware-controlled processing units may be used in place of or incombination with processor 504 and its associated computer softwareinstructions to implement the invention. The computer-readableinstructions may be rendered in any computer language.

In general, all of the above process descriptions are meant to encompassany series of logical steps performed in a sequence to accomplish agiven purpose, which is the hallmark of any computer-executableapplication. Unless specifically stated otherwise, it should beappreciated that throughout the description of the present invention,use of terms such as “processing”, “computing”, “calculating”,“determining”, “displaying”, “receiving”, “transmitting” or the like,refer to the action and processes of an appropriately programmedcomputer system, such as computer system 500 or similar electroniccomputing device, that manipulates and transforms data represented asphysical (electronic) quantities within its registers and memories intoother data similarly represented as physical quantities within itsmemories or registers or other such information storage, transmission ordisplay devices.

Computer system 500 also includes a communication interface 518 coupledto the bus 502. Communication interface 518 may provide a two-way datacommunication channel with a computer network, which providesconnectivity to and among the various computer systems discussed above.For example, communication interface 518 may be a local area network(LAN) card to provide a data communication connection to a compatibleLAN, which itself is communicatively coupled to the Internet through oneor more Internet service provider networks. The precise details of suchcommunication paths are not critical to the present invention. What isimportant is that computer system 500 can send and receive messages anddata through the communication interface 518 and in that way communicatewith hosts accessible via the Internet.

Thus, methods and systems for photocuring liquid resin with reduced heatgeneration using a DLP light source have been described. It is to beunderstood that the above-description is intended to be illustrative,and not restrictive. Many other embodiments will be apparent to those ofskill in the art upon reviewing the above description. The scope of theinvention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled.

What is claimed is:
 1. A vat polymerization printer, comprising: a tankconfigured for containing a photo-curable liquid resin, the tankincluding a tank opening; a digital light processing (DLP) light sourceconfigured to project light towards the tank opening; a liquid crystaldisplay (LCD) mask disposed between the DLP light source and the tankopening, the mask having pixels configurable to be individuallytransparent or opaque to portions of the light projected from the DLPlight source; and a controller configured to control the DLP lightsource to project the light with varying intensity such that portions ofthe light with high intensity are transmitted through one or morerespective transparent pixel regions of the mask and onto opaque pixelsat perimeters of the one or more transparent pixel regions of the maskand portions of the light with low intensity are blocked by respectiveopaque pixels of the mask.
 2. The vat polymerization printer of claim 1,wherein the mask is disposed adjacent to the tank opening.
 3. The vatpolymerization printer of claim 1, wherein the mask comprises atwo-dimensional array of the configurable pixels.
 4. The vatpolymerization printer of claim 3, wherein the controller is configuredto control the DLP light source and the mask.
 5. The vat polymerizationprinter of claim 4, wherein the controller is further configured tosynchronize an operation of the DLP light source with an operation ofthe mask.
 6. The vat polymerization printer of claim 1, wherein aspatial resolution of the mask is greater than a spatial resolution ofthe DLP light source.
 7. The vat polymerization printer of claim 1,further comprising a radiation-transparent flexible membrane disposedacross the tank opening.
 8. The vat polymerization printer of claim 7,further comprising an extraction plate configured to translate apartially formed object within the tank in a direction perpendicular toan extent of the radiation-transparent flexible membrane.
 9. The vatpolymerization printer of claim 1, wherein the DLP light sourcecomprises a DLP projector.
 10. The vat polymerization printer of claim1, wherein the DLP light source comprises a digital micromirror device(DMD).
 11. The vat polymerization printer of claim 1, wherein the maskis configured to enhance a resolution of the DLP light source.
 12. Amethod, comprising: projecting, via a digital light processing (DLP)light source, light towards an opening in a tank containingphoto-curable liquid resin; filtering, by a liquid crystal display (LCD)mask, the light from the DLP light source, the mask having pixelsconfigurable to be individually transparent or opaque to portions of thelight projected from the DLP light source; and in a build area of thetank, curing the photo-curable liquid resin with the filtered light fromthe DLP light source so as to form a layer of a partially formed object,wherein the light is projected from the DLP light source with varyingintensity such that portions of the light with high intensity aretransmitted through one or more respective transparent pixel regions ofthe mask and onto opaque pixels at perimeters of the one or moretransparent pixel regions of the mask and portions of the light with lowintensity are blocked by respective opaque pixels of the mask.
 13. Themethod of claim 12, further comprising translating, by an extractionplate, the partially formed object in a direction perpendicular to anextent of the mask.
 14. The method of claim 12, wherein the maskcomprises a two-dimensional array of the configurable pixels.
 15. Themethod of claim 12, wherein the projection of light from the DLP lightsource is synchronized with the filtering of the light by the mask. 16.The method of claim 12, wherein a spatial resolution of the mask isgreater than a spatial resolution of the DLP light source.
 17. Themethod of claim 12, wherein the DLP light source comprises a DLPprojector.
 18. The method of claim 12, wherein the DLP light sourcecomprises a digital micromirror device (DMD).
 19. The method of claim12, wherein the individually transparent or opaque pixels are providedsuch that the projection of light from the DLP light source imparts lessthan 10% of a peak radiation of the projected light onto the opaquepixels of the mask and greater than 90% of the peak radiation of theprojected light onto the transparent pixels.
 20. The method of claim 12,wherein the mask enhances a resolution of the DLP light source.